1. Field of the Invention
The present invention relates to rotary piston engines, and more particularly to intake systems for rotary piston engines. More specifically, the present invention pertains to side port type intake systems for two-rotor rotary piston engines.
2. Description of Prior Art
In general, a rotary piston engine includes a casing comprised of a rotor housing having an inner wall of trochoidal configuration, and a pair of side housings secured to the opposite sides of the rotor housing to define a rotor cavity in the rotor housings. A rotor of substantially polygonal configuration is disposed in the rotor cavities and has flanks which define, with the inner wall of the rotor housing, working chambers having volumes which are cyclically changed as the rotor rotates. The casing is generally formed with an exhaust and intake ports so that intake, compression, combustion, expansion and exhaust cycles are conducted sequentially in each of the working chambers.
In this type of rotary piston engines, it has been proposed to utilize pulsations in the intake passage so that effective feed of intake gas can be accomplished throughout a wide range of the engine operating speed. For example, the U.S. Pat. No. 3,491,733 issued on Jan. 27, 1970 to Soubis et al. teaches to separate the intake passage into two passages of different lengths and connect these separated passages to two separated intake ports having different port closing timings so that the two passages and the two intake ports are used under a high speed engine operation whereas only one passage and only one intake port having earlier port closing timing are used under a low speed engine operation. With this arrangement, it is possible to feed the intake charge with resonance under a wide engine operating speed.
It should however be noted that the U.S. patent relates to a single rotor type rotary piston engine and there is no precise teaching as to how the pulsations in the passages are utilized. Further, the U.S. patent discloses a so-called peripheral port type rotary piston engine having the intake ports provided in the rotor housing. This type of engine is considered disadvantageous in that the intake ports are overlapped with the exhaust port so that the exhaust gas is blown under its own pressure into the intake working chamber decreasing the intake gas charge. In engines of recent years, there is a tendency that the exhaust gas pressure is increased due to facilities for suppressing engine noise and for purifying engine exhaust gas. In engines having turbo-superchargers, the exhaust gas pressure is further increased. Therefore, the peripheral port type intake system is not satisfactory to increase the intake charge utilizing the resonance effect.
In view of the foregoing problems, the inventors have proposed by the application Ser. No. 542,584 filed on Oct. 17, 1983 an intake system for two-rotor type rotary piston engines in which pulsations in intake passages can effectively be utilized to increase the intake gas charge. The proposal is based on the findings that a compression wave is produced in the vicinity of the intake port when the port is opened under the influence of the pressure of the residual combustion gas and that there is a tendency in recent engines that the compression wave is intensified due to the increase in the exhaust gas pressure. According to the proposal, the arrangement is such that in two rotor rotary piston engines, the compression wave produced in one intake passage leading to one rotor cavity when the intake port for the same rotor cavity is opened is transmitted through the other intake passage leading to the other rotor cavity to the intake port of the said other rotor cavity just before the latter mentioned intake port is closed under a specific engine speed.
The proposed arrangement is considered to be effective in providing an increased intake charge under the specific engine speed. It should however be noted that, when the intake system is applied to fuel injection type engines having airflowmeters and fuel injection valves for supplying metered amount of fuel in accordance with the airflow signals from the airflowmeters, it is required to provide surge tanks in the intake passages in order to avoid undesirable changes in the air-fuel ratio during transient periods of engine operations. Such surge tanks in the intake passages have been found as having effects of absorbing pressure pulsations in the intake passages so that the supercharging effects of the proposed arrangements are decreased.